This invention relates to electric motor assembly, and in particular to electric motor assembly for washing machine applications. While the invention is described in particular detail to such applications, those skilled in the art will recognize the applicability of the inventive concepts disclosed hereinafter.
In known washing machine applications, a drive motor for the machine is mounted vertically on or near the underside of the wash tub of the machine. Conventionally, the motor is mounted to a mounting plate through a suitable arrangement, which, in the application with which I am familiar, mounts the motor through at least the most remote, with respect to the mounting plate, endshield of the motor. The mounting plate also holds an adjacent transmission assembly, the shaft of which also passes through the mounting plate to a pulley which is driven by a belt from a pulley on the shaft of the electric motor. The transmission has a shaft extending vertically upward into the tub assembly of the washing machine to turn the agitator and to cause the spinning of the clothes tub. In the typical applications, the motor and transmission mounting arrangement suspends these assemblies in such a way that they are often subjected to a considerable amount of interactive vibration and wobbling movements. In addition, the operating environment is a consideration which must be addressed when designing motor assemblies for use in such applications. The heat added to the immediate environment of the motor from the washing operation, where hot water is used, plus the heat generated by the motor itself are factors which must be addressed in the motor design. The size of machine, specifically in relation to the washing load that will be handled under maximum load conditions, is an additional factor which must be considered in sizing the motor. Generally, only a limited amount of space exists between the bottom of the wash tub and the top of the mounting plate which supports the transmission and the motor. The available and limited space also must accommodate the pulleys on the shafts of the transmission and motor, which are mounted below the mounting plate. The total distance between the bottom of the wash machine cabinet or enclosure supporting surface and the tub bottom are design constraints that must be considered when designing a motor for the purpose of providing the appropriate level of performance to accommodate wash loads, and configuring the motor for the purpose of heat management in the washing machine environment.
It has been found that even the selection of materials, particularly those used in the endshields of the motor assembly, can contribute in a positive way, not only in addressing the heat management issues of the motor design, but also the size and configuration issues related to the limited space available in the operating environment. with respect to the issue of material selection, it has been found that when sheet metal, and specifically sheet steel, is pressed to produce endshields with bearing housings integral with the endshields, the bearing housings typically extend axially outward and along the motor arm, further limiting the space available for actual motor configuration and eventual operation. Where, as in the present invention, cast aluminum is used, the bearing housings, if required, can be made internal of the endshield, and thus, not infringe upon the limited space available between the tub and adjacent endshield. The saving of such otherwise wasted space can thus be more effectively utilized by the motor design. As indicated above, as used herein, "sizing" relates to designing the motor so that it has adequate power to handle the wash loads intended, and that relates directly to stator/rotor assembly lamination size, stack height, and the motor winding design for the motor necessary to achieve the required electrical performance. These dimensional factors are matters of great concern in view of the space limited environment in which the motor is required to operate.
It is also known that the reliability and life expectancy of the motor and its effectiveness in the application can be greatly effected by the way the motor is mounted.
An example of a mounting approach employed in prior art application designs for similar size washing machine requirements employs a mounting bracket for securing the motor to the mounting plate. The mounting plate also accommodates the transmission for the washing machine. The design uses an extension of the endshield positioned furthermost from the motor which is positioned closest to the bottom of the tub. In this known design spacing blocks are used between the bracket and the mounting plate in conjunction with long mounting bolts to make the physical connection to the mounting plate.
One problem with this mounting approach is that by placing the mounting bracket of the motor at the end remote from the mounting plate and using elongated bolts for mountings, the motor is much more susceptible to wobbling and vibration induced by its own operation, and by mechanical feedback from and through the transmission, even when the transmission is shock mounted to the mounting plate. The belt drive pulley system for powering the transmission through the motor, located on the bottom side of the mounting plate, subjects the motor mounted with the spacer blocks and long mounting bolts to considerable rotational force about the mounting plate, or thrust, which would not otherwise exist if the mounting were made directly from one or the other of the endshields to the mounting plate without the spacer blocks and long bolts. Consequently, prior art motor designs required the thrust system to compensate for the forces exerted by system operation.
It is thus an object of the present invention to reduce overall motor size, and particularly to limit the length of the motor from front to back so that it may be used in limited space applications such as a washing machine. It is yet another object of the present invention to reduce the motor size to provide more air circulation in the application space. It is another object of the present invention to provide a motor design that permits a motor mounting system that has greater motor stability and less wobble. Yet another object of the present invention is to provide a motor and mounting design that permits more secure mounting and maintenance of coplanar pulley positions for belt driving a washing machine transmission from an electric motor mounted adjacent to the transmission. It is yet another object of the present invention to select materials for fabrication of an electric motor for use in a washing machine and limited space application environment such that motor size advantages and cooling advantages may be obtained. It is still another object of the present invention to permit motor size increase that is independent of the mounting system used to attach the motor to the transmission that the motor must drive in a washing machine application. Yet another object of the present invention is to provide a mounting system that holds the distance between the motor mounting means and the mounting plate that is used to hold the motor relative to the washing machine at a minimum relative to the shaft end of the motor. Another object of the present invention is to provide a simple, easily producible motor mounting system that permits stable power communication by means of a belt and pulley system to a washing machine transmission secured to the same mounting plate in the tight spaced environment below the washtub of a washing machine.